Table 8-34 shows the functions available to query and alter run-time configuration parameters.
Table 8-34. Configuration Settings Functions
| Name | Return Type | Description |
|---|---|---|
current_setting(setting_name)
| TEXT | current value of setting |
set_config(setting_name,
new_value,
is_local)
| TEXT | set parameter and return new value |
The function current_setting yields the
current value of the setting setting_name.
It corresponds to the SQL command
SHOW. An example:
SELECT current_setting('datestyle');
current_setting
-----------------
ISO, MDY
(1 row)
set_config sets the parameter
setting_name to
new_value. If
is_local is true, the
new value will only apply to the current transaction. If you want
the new value to apply for the current session, use
false instead. The function corresponds to the
SQL command SET. An example:
SELECT set_config('log_statement_stats', 'off', false);
set_config
------------
off
(1 row)
The function shown in Table 8-35 sends control signals to other server processes. Use of this function is restricted to superusers.
Table 8-35. Backend Signalling Functions
| Name | Return Type | Description |
|---|---|---|
pg_cancel_backend(pid)
| INT | Cancel a backend's current query |
This function returns 1 if successful, 0 if not successful. The process ID (pid) of an active backend can be found from the procpid column in the pg_stat_activity view, or by listing the edb-postgres processes on the server with ps.
The functions shown in Table 8-36 assist in making on-line backups. Use of these functions is restricted to superusers.
Table 8-36. Backup Control Functions
| Name | Return Type | Description |
|---|---|---|
pg_start_backup(label_text)
| TEXT | Set up for performing on-line backup |
pg_stop_backup()
| TEXT | Finish performing on-line backup |
pg_start_backup accepts a single parameter which is an
arbitrary user-defined label for the backup. (Typically this would be
the name under which the backup dump file will be stored.) The function
writes a backup label file into the database cluster's data directory,
and then returns the backup's starting WAL offset as text. (The user
need not pay any attention to this result value, but it is provided in
case it is of use.)
pg_stop_backup removes the label file created by
pg_start_backup, and instead creates a backup history file in
the WAL archive area. The history file includes the label given to
pg_start_backup, the starting and ending WAL offsets for
the backup, and the starting and ending times of the backup. The return
value is the backup's ending WAL offset (which again may be of little
interest).
For details about proper usage of these functions, see Section 27.3.